This invention relates to a bow saw machine which has a saw blade tensioned obliquely with respect to the direction in which the saw bow is guided (reciprocated) and a machine frame, on the work table of which the workpiece is immobilized by means of clamping jaws during the sawing operation. At least one of the clamping jaws is displaceably mounted. The back of the saw bow is enlarged twice in a web-like manner on both sides in a direction transverse to the reciprocating motion of the saw bow. The ends of the webs of the saw bow are displaceably supported on a housing which is, in turn, pivotally supported on the machine frame for swinging in a substantially vertical plane. The bow saw machine further has a saw bow drive constituted by a motor-driven crank drive coupled to the saw bow and arranged about the back of the saw bow substantially within the zone of saw bow stroke (path of reciprocation). The rotary axis of the rotary shaft of the crank drive extends substantially in a vertical direction and lies in, or is parallel to, the plane of the saw blade. The drive shaft carries an eccentric crank pin which projects into a guide groove provided on the back of the saw bow. The guide groove extends parallel to the above-noted web-like enlargements.
A bow saw machine of the above-outlined type is known and is disclosed, for example, in German Published Accepted Patent Application (Auslegeschrift) No. 2,262,957. This bow saw machine accomplishes the object of reducing the spatial requirement in the direction of reciprocation, practically to the length of the saw bow including the length of its stroke while, at the same time, providing for a high sawing efficiency. In essence, this is achieved by arranging the crank drive above the saw bow such that its drive shaft is arranged perpendicularly to the saw bow. If, however, it is desired to equip such a bow saw machine with a hydraulic device for an automatic setting of the saw blade on the workpiece (setting of the cutting depth for the successive work stroke) as well as for the regulation of the sawing pressure, difficulties are encountered because such a hydraulic setting device constitutes a coupling between the machine frame and the pivotal housing and further, it cooperates with the crank drive. But, in the above-described structure, the saw bow and its travelling path are positioned in such a manner that they would constitute an obstruction for such a cooperation. Since the connection between the crank drive and the saw bow is effected in most cases by means of an eccentric arranged on the crank shaft, the above-noted vertical position of the crank shaft gives rise to the further difficulty that the eccentric would lie and be effective substantially in a horizontal plane, thus not allowing a generation of the substantially vertical pivotal motion of the housing that contains the saw bow guide.
Regarding the above-mentioned device for setting the saw blade in the direction of the workpiece (feed setting) as well as for providing the sawing pressure, reference is made to the disclosure in German Pat. No. 1,068,086. The device described therein comprises in essence a double-acting cylinder-and-piston assembly, the bilateral cylinder chambers of which are coupled to one another by a fluid transfer conduit in which there is arranged an adjustable throttle valve with which the setting of the saw blade in the direction of the workpiece can be adjusted. This is accomplished by providing that during the idling stroke, the piston is lowered to a greater or lesser extent under the weight of the pivotal machine component. During the work stroke, the piston is exposed to the sawing pressure in the opposite direction. During this occurrence a sawing pressure valve which adjoins a cylinder chamber then pressurized, provides that the desired sawing pressure is not exceeded. This is achieved by ensuring that from the pressurized cylinder chamber the pressurized medium may flow into a sump (depressurized reservoir) through the sawing pressure valve.